<template>
  <div>
    <router-link tag="div" to="/" v-show="showAbs" class="header-abs">
      <span class="iconfont back-arrow">&#xe743;</span>
    </router-link>
    <div class="header-fixed" v-show="!showAbs" :style="opacityStyle">
      <router-link to="/">
        <span class="iconfont back-arrow">&#xe743;</span>
      </router-link>
      景点详情
    </div>
  </div>
</template>
<script>
export default {
  name: "DetailHeader",
  data() {
    return {
      showAbs: true,
      opacityStyle: {
        opacity: 0,
      },
    };
  },
  methods: {
    handleScroll() {
      //当页面滑动到指定高度时候控制对应的返回显示或隐藏
      const top = document.documentElement.scrollTop;
      if (top > 60) {
        let opacity = top / 140;
        opacity = opacity > 1 ? 1 : opacity;
        this.opacityStyle = {
          opacity,
        };
        this.showAbs = false;
      } else {
        this.showAbs = true;
      }
    },
  },
  activated() {
    //在vue对象存活的情况下，进入当前存在activated()函数的页面时，一进入页面就触发；可用于初始化页面数据等
    window.addEventListener("scroll", this.handleScroll);
  },
  deactivated() {
    //解绑全局事件，执行完就销毁上面的周期函数
    window.removeEventListener("scroll", this.handleScroll);
  },
};
</script>
<style scoped lang="stylus">
@import '~style/var.styl'
  .header-abs
    position: absolute
    left: .2rem
    top: .2rem
    width: .8rem
    height: .8rem
    line-height: .8rem
    border-radius: .4rem
    text-align: center
    background: rgba(0, 0, 0, .8)
    .header-abs-back
      color: #fff
      font-size: .4rem
  .header-fixed
    z-index: 2
    position: fixed
    top: 0
    left: 0
    right: 0
    height: $headerHeight
    line-height: $headerHeight
    text-align: center
    color: #fff
    background: $bgColor
    font-size: .32rem
    .header-fixed-back
      position: absolute
      top: 0
      left: 0
      width: .64rem
      text-align: center
      font-size: .4rem
      color: #fff
</style>
